NARRATIVE OF THE CRUISE 



225 



on the depth from which the deposit was collected — a check which 

 would be more reliable than that offered by the length of wire 

 paid out and the angle. Due to the drift of the vessel and cross- 

 currents in the deeps, the wire almost never dropped in a straight 

 line to the bottom. We were able to calculate depths accurately 

 from the difference between the readings of two reversing-ther- 

 mometers sent down together. One of them was protected against 

 the enormous pressures at great depths to give the true tempera- 

 ture; the other, being unprotected, gave a reading which repre- 

 sented the temperature plus the mechanical "squeezing" of the 

 mercury bulb due to the weight of the water-column above it. 



A Propeller-device for Reversing Deep-sea Thermometers 



This is attached to the bottom-sampling wire, and when the sampler is hauled in the 

 propeller turns and releases the pin which holds the thermometers upright as they plunge 

 to the bottom — temperatures of the ocean-bottom have rarely been measured, although 

 they are of great interest to oceanographers. 



Our echo-sounding device gave us a third check on bottom- 

 depths, of course. In scientific work such as we were doing, 

 there are never too many checks. Even the simplest procedure 

 is subject to error at times; and our aim was to attain the highest 

 degree of accuracy possible in every measurement made on board. 



During heavy weather we often found our silk tow-nets torn 

 by a sudden surge of the vessel. These nets were very expensive, 

 and had to be made to order in Washington. So we made every 

 effort to save them. On February 18, we tried attaching the 

 nets to the ship by a long rubber rope commonly used in the 

 landing gear of air-craft. Afterwards, we seldom lost a net. In 

 addition, after February 6, the plankton-tows were made from 

 the forecastle head, thus reducing the danger of fouling the other 

 wires which were lowered from the quarter-deck. 



